A Million Turnover Molecular Anode for Catalytic Water Oxidation

Molecular ruthenium-based water oxidation catalyst precursors of general formula [Ru(tda)(Lⁱ)₂] (tda²⁻ is [2,2′:6′,2′′-terpyridine]-6,6′′-dicarboxylato; L¹=4-(pyren-1-yl)-N-(pyridin-4-ylmethyl)butanamide, 1 b; L²=4-(pyren-1-yl)pyridine), 1 c), have been prepared and thoroughly characterized. Both complexes contain a pyrene group allowing ready and efficiently anchoring via π interactions on multi-walled carbon nanotubes (MWCNT). These hybrid solid state materials are exceptionally stable molecular water-oxidation anodes capable of carrying out more than a million turnover numbers (TNs) at pH 7 with an E_app=1.45 V vs. NHE without any sign of degradation. XAS spectroscopy analysis before, during, and after catalysis together with electrochemical techniques allow their unprecedented oxidative ruggedness to be monitored and verified.